Fungi Mimicry – The being is some type of fungus. Mushrooms are a type of fungus.
In Supergod #1 (Avatar) a three-faced giant formed from the bodies of three astronauts and a mass of alien mushrooms act as a fungal supercomputer.
Campestri – TSR 2145 Monstrous Compendium Annual Volume 1
Chromatic Mold – TSR 2173 Monstrous Compendium Annual Volume 4
Fungi from Yuggoth – Field Guide to Cthulhu Monsters
Fungus – Helmet of Fate – Zauriel #1
Fungus – TSR 2140A Monstrous Manual
Golgotha (Marvel) – OHOTMU A – Z Update #4
Mold – Star Trek DS9 #2 (Malibu)
Mold Man – TSR 2140A Monstrous Manual
Mold – TSR 2140A Monstrous Manual
Myconid – D&D 4th Edition – Monster Manual 2
Phantom Fungus – D&D 3.5 – Monster Manual I
Violet Fungus – D&D 3.5 – Monster Manual I
Spider Woman (Marvel) humorously deals with a mushroom monster on the Moon in Spider-Woman V5 #10.
TCG Zombie Mushrooms are extremely cute!